Gas purification apparatus and gas purification method

ABSTRACT

The present invention is intended to provide a gas purification apparatus and a gas purification method with an excellent thermal efficiency and capable of degrading COS at a high degradation rate. A gas purification apparatus configured to purify gas at least including COS, H 2 O, CO 2 , and H 2 S includes a COS treatment device which is provided with a COS conversion catalyst and configured to treat and degrade COS in the gas by hydrolysis, and H 2 O adjustment means configured to adjust the concentration of H 2 O in the gas to be introduced into the COS treatment device.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a gas purification apparatus and a gaspurification method capable of promoting a treatment for degrading COSby adjusting the concentration of H₂O in material gas.

2. Background Art

As one of the ultimate solutions to energy issues arising in recentyears, effective utilization of coal has attracted much attention. Toconvert coal into an energy medium with a high additional value such asmethanol and ammonia, advanced techniques are used such as a techniquefor gasifying coal and a technique for purifying gas obtained bygasifying coal.

Sulfur is commonly contained in coal, and when coal is gasified, the gasincludes sulfur compounds such as carbon oxysulfide (COS) and hydrogensulfide (H₂S). If this gasified gas is burned without removing suchsulfur compounds, the burned compounds will be discharged into theatmosphere as sulfur oxides, which can cause acid rain and environmentaldamage. Although wet gas purification processes in which H₂S is removedby using amine-based aqueous solutions have been commercialized asmethods for removing such sulfur compounds, COS cannot be removed byusing amine-based aqueous solutions.

To solve this problem, a catalytic reaction process has been proposed inwhich COS is degraded by a hydrolytic reaction process expressed by thefollowing expression (2) and converted into H₂S, which can be removed byusing an amine-based aqueous solution (e.g., Patent Literature 1).

[Expression 1]

COS+H₂O→H₂S+CO₂  (2)

Because COS degradation reactions are hydrolytic, if the concentrationof H₂O in material gas is high, COS can be degraded at a higherdegradation rate. In the gas purification apparatus discussed in PatentLiterature 2, for example, gasified gas discharged from a gasificationfurnace is introduced into a COS converter via a water washing column todegrade COS and is then fed into an absorption column to remove H₂Stherefrom. In the water washing column, impurities in the gasified gasare recovered and the concentration of H₂O in the gasified gasincreases, and therefore, COS is easily degraded in the COS converter.However, it is necessary to cool the gasified gas heated in thegasification furnace for water washing in the water washing column andthen heat the cooled gasified gas again up to a temperature suitable fordegradation of COS. As described above, because processes for heatingand cooling gasified gas are repeated in a gas purification apparatus,the facility configuration may be complex, and also, the thermalefficiency of the configuration of the processes may be low.

On the other hand, the gas purification apparatus described in PatentLiterature 3, for example, has an apparatus configuration in whichgasified gas discharged from a gasification furnace is introduced into aCOS treatment device for degradation of COS and is then fed into a waterwashing column. The gasified gas having been heated in the gasificationfurnace is cooled by a heat exchanger to a temperature suitable fordegradation of COS, and after COS has been degraded, the gas is furthercooled to a temperature suitable for washing with water. As describedabove, the gas purification apparatus does not repeat heating andcooling of gasified gas, which realizes a process configuration with anexcellent thermal efficiency. However, because the gasified gasdischarged from the gasification furnace is introduced into the COStreatment device without adjusting the concentration of H₂O, theconcentration of H₂O in the gasified gas depends on gasificationconditions for the gasification furnace. Therefore, it is difficult toalways degrade COS at a high degradation rate.

CITATION LIST Patent Literature

-   Patent Literature 1: JP 4594886 B1-   Patent Literature 2: JP 3688922 B1-   Patent Literature 3: JP 4467872 B1

SUMMARY OF INVENTION Technical Problem

In order to solve the above-described problems, the purpose of thepresent invention is to provide a gas purification apparatus and a gaspurification method with an excellent thermal efficiency capable ofdegrading COS at a high degradation rate.

Solution to Problem

In order to solve the above-described problems, the inventor hasconducted various research to improve the COS degradation rate withoutdecreasing the thermal efficiency. The inventor has thus found that COScan be degraded at a high degradation rate without decreasing thethermal efficiency by adjusting the concentration of H₂O beforehydrolytic degradation of COS, and the present invention has beencompleted on the basis of this finding.

In other words, in a first embodiment according to the presentinvention, a gas purification apparatus is configured to purify gas thatat least includes COS, H₂O, CO₂ and H₂S, the gas purification apparatusat least being provided with a COS treatment device including a COSconversion catalyst and being configured to degrade COS in the gas byhydrolysis, and H₂O adjustment means configured to adjust theconcentration of H₂O in the gas to be introduced to the COS treatmentdevice.

In a second embodiment of the present invention, a gas purificationmethod for purifying gas which at least includes COS, H₂O, CO₂, and H₂S,the gas purification method includes an H₂O adjustment step of adjustingthe concentration of H₂O in the gas, and a COS treatment step ofdegrading COS in the gas, the gas of which the concentration of H₂O hasbeen adjusted, by hydrolysis by using a COS conversion catalyst.

Advantageous Effects of Invention

According to the present invention, COS can be degraded at a highdegradation rate without decreasing thermal efficiency.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an outline view of a gas purification process.

FIG. 2 is an outline view of a gas purification process that includes awater washing column and the like in addition to the gas purificationprocess illustrated in FIG. 1.

FIG. 3 is an outline view of a gas purification process of an embodimentdifferent from those illustrated in FIGS. 1 and 2.

FIG. 4 is an outline view of a gas purification process of an embodimentdifferent from those illustrated in FIGS. 1 to 3.

FIG. 5 is an outline view of a gas purification process of an embodimentthat includes all the H₂O adjustment means illustrated in FIGS. 1 to 4.

FIG. 6 is a diagram that illustrates an example of a gas purificationapparatus of the present invention.

DESCRIPTION OF EMBODIMENTS

General embodiments of the present invention will be described in detailbelow.

To begin with, a gas purification apparatus of the present invention isan apparatus configured to purify gas that at least includes COS, H₂O,CO₂, and H₂S. Examples of gas that includes such compounds include gasesobtained by gasifying coal, oil, biomass, and the like. Gas to bepurified by the present invention may include CO, N₂, HCl, O₂, and thelike in addition to the compounds described above.

The gas purification apparatus of the present invention at leastincludes a COS treatment device and H₂O adjustment means. The COStreatment device is a device that includes a COS conversion catalyst andconfigured to treat and degrade COS in the gas to be purified byhydrolysis. For the COS treatment device, a device in which a COSconversion catalyst has been loaded in an inside of a reactor, a devicein which a combination of an O₂ removal catalyst and a COS conversioncatalyst has been loaded in a reactor, and a COS conversion catalystthat also includes an O₂ removal function has been loaded in a reactorcan be used. For the COS conversion catalyst, a catalyst that includestitania, chromium, and alumina can be generally used.

The H₂O adjustment means of the gas purification apparatus according tothe present invention is a means configured to adjust the concentrationof H₂O in the gas to be introduced into the COS treatment device. COScan be degraded at a high degradation rate by adjusting theconcentration of H₂O in gas to be purified before hydrolytic degradationof COS by using the COS conversion catalyst.

It is preferable that the H₂O adjustment means of the gas purificationapparatus according to the present invention be a means configured toadjust the H₂O concentration so that a pressure equilibrium constantK_(P) expressed by the following Expression (1) becomes 1≦K_(P)≦20 whereP_(COS) is a partial pressure of COS in the gas, P_(H2O) is a partialpressure of H₂O in the gas, P_(CO2) is a partial pressure of CO₂ in thegas, and P_(H2S) is a partial pressure of H₂S in the gas.

[Expression 2]

K _(P)=(P _(H2S) ×P _(CO2))/(P _(COS) ×P _(H2O))  (1)

COS hydrolytic reactions are a reversible reaction, and if K_(P) is 20or smaller, hydrolysis of COS easily progresses, and thus, COS can bedegraded at a high degradation rate. If K_(P) is 10 or less, COS can bemore quickly degraded. COS can be degraded in an excellent manner evenwhen K_(P) is as small as 1; however, a range of K_(P) below 1 isdisadvantageous to hydrolysis of COS in terms of equilibrium, and thus,it becomes difficult for hydrolysis of COS to progress in this range ofK_(P).

The pressure equilibrium constant can be theoretically varied byadjusting not only the partial pressure of H₂O but also the partialpressures of COS, CO₂, and H₂S. However, the ratios of COS, CO₂, and H₂Sare fixed depending on the raw stock to be gasified and based ongasification conditions or the like. Therefore, in order to vary theratio of these compounds, a method should be used in which COS, CO₂, orH₂S is individually mixed with gasified gas, for example. However,because COS and H₂S are compounds to be recovered, it is not preferableto increase the amount thereof. Furthermore, it is not efficient to mixCO₂ with the gas for adjustment of the pressure equilibrium constantonly, considering the cost of purchase of CO₂, and because it becomesnecessary to separately install additional facilities. Among COS, H₂O,CO₂, and H₂S, the amount of H₂O can be easily adjusted by changing theconditions for drying raw stock such as coal or by mixing H₂O withgasified gas, for example. Accordingly, in the present invention,adjustment of H₂O is the most effective means for varying the pressureequilibrium constant.

The gas purification apparatus of the present invention can furtherinclude at least one water washing device and at least one waste watertreatment device. The water washing device is a device for washing thegas discharged from the COS treatment device with water and isconfigured to remove impurities, such as water-soluble halogencompounds, ammonia, organic matters, and trace metals by washing withwater. It is preferable that the gas purification apparatus include aplurality of water washing devices that are preferably arranged inseries. It is difficult to completely remove impurities by using onewater washing device only, and by providing the plurality of waterwashing devices for removal of impurities, the purity of the gas can beincreased. If a plurality of water washing devices is included, devicesof the same shape can be used for the water washing devices.

The waste water treatment device is a device configured to treat wastewater drained from the water washing device so that the waste waterincluding the impurities that have been removed from the gas by washingwith water can be disposed of. More specifically, the impurities aretreated by using a device configuration including an ammonia strippingcolumn and a flocculating precipitation device. Waste water drained fromone water washing device can be treated by one waste water treatmentdevice. Furthermore, waste water drained from a plurality of waterwashing devices can be treated by one waste water treatment device.Furthermore, waste water drained by at least one or more water washingdevices can be treated by a plurality of waste water treatment devices.

If the gas purification apparatus of the present invention includes thewater washing device and the waste water treatment device, the H₂Oadjustment means can be means configured to mix water from the wastewater treatment device with gas to be introduced into the COS treatmentdevice. If a feed line for feeding water from the waste water treatmentdevice is connected to an introduction line for introducing gas into theCOS treatment device, and if a control means configured to control theamount of water to be fed in accordance with the composition of the gasis further provided, for example, then H₂O can be adjusted by mixing thewater from the waste water treatment device with the gas. By using theabove-described means, water used in the gas purification process can becirculated and reused multiple times without introducing H₂O from anoutside of the gas purification apparatus, and thus, the facilityconfiguration of the gas purification apparatus can be simplified.

If the gas purification apparatus of the present invention is providedwith a plurality of waste water treatment devices, it is preferable thatthe water from the waste water treatment device that treats waste waterincluding less impurities be mixed with the gas. Halogen compounds maybe contained in the gas to be purified as impurities, and the halogencompounds may be one of the causes of shorter life of COS conversioncatalysts. If halogen compounds contained in the waste water are furtherpresent in the gas in addition to the existing halogen compounds in thegas, the life of the COS conversion catalyst may be further shortened.By mixing water from the waste water treatment device that treats wastewater including less impurities with the gas, effects on the COSconversion catalyst can be suppressed to the minimum.

In the gas purification apparatus of the present invention, the H₂Oadjustment means can be a means configured to mix steam with gas to beintroduced into the COS treatment device. If a feed line for feedingsteam from a steam feed means is connected to an introduction line forintroducing gas to the COS treatment device, and if a control meansconfigured to control the amount of water to be fed in accordance withthe composition of the gas is further provided, for example, then H₂Ocan be adjusted by mixing the steam with the gas. Examples of the steamfeed means include steam bleeding from boilers or steam turbines. If thesteam feed means is a means that constitutes the gas purificationapparatus, the facility configuration of the gas purification apparatuscan be simplified without introducing H₂O from an outside of the gaspurification apparatus. The means for mixing steam with the gas to beintroduced into the COS treatment device can be used in combination withthe above-described means for mixing water from the waste watertreatment device with the gas to be introduced into the COS treatmentdevice.

The gas purification apparatus of the present invention can be furtherprovided with a coal drying device and a gasification furnace. The coaldrying device is a device configured to dry coal by removing moisturecontent from the coal, and coal drying devices such as ahigh-temperature flue gas heating type device, a rotational dryer typedevice, a steam fluidized bed type device, and a mechanical pressingtype device can be used as the coal drying device. If coal is used asthe raw stock of the gas to be purified and if the coal includesexcessive moisture content, the gasification efficiency may decrease. Toprevent this, in gasification of coal, the coal drying device is used tomaintain the moisture content in the coal at a predetermined amount sothat the gasification efficiency will not decrease. In drying coal, heatfrom the flue gas generated in the gas purification processes can beused, and alternatively, the coal can be dried by using heat introducedinto the coal drying device from outside of the gas purificationapparatus.

The gasification furnace is a furnace configured to gasify the driedcoal. The coal dried by the coal drying device and oxygen, air, andoxygen-enriched air as gasification agents are deposited into thegasification furnace, and gasified gas is extracted by pyrolysis.

If the gas purification apparatus of the present invention is providedwith the coal drying device and the gasification furnace, the H₂Oadjustment means can be a means configured to adjust the moisturecontent in the coal by using the coal drying device. H₂O can be adjustedby controlling the moisture content in the coal before being gasified byproviding measurement means configured to measure the moisture contentin gasified gas in the gasification furnace and by further providingadjustment means configured to adjust the amount of heat to beintroduced into the coal drying device and drying time for drying coalin accordance with the moisture content. It is important to consider thegasification efficiency in controlling the moisture content in the coal.By using the above-described means, H₂O can be adjusted by using anexisting coal drying device and a gasification furnace withoutinstalling additional facilities to correspond to an nonstationary statein which the concentration of COS in the gasified gas has abruptlyincreased.

The means for adjusting the moisture content in coal by using the coaldrying device can be used in combination with the above-described meansfor mixing steam with the gas to be introduced into the COS treatmentdevice and the above-described means for mixing water from the wastewater treatment device with the gas to be introduced into the COStreatment device.

In addition to the above-described devices, the gas purificationapparatus of the present invention can further include devices such as adust collecting device configured to remove dust from the gas, a heatexchanger configured to adjust the temperature of the gas, an H₂Sabsorption column configured to recover H₂S from the gas, and anabsorbing solution regeneration column configured to regenerate theabsorbing solution that has absorbed H₂S.

According to the gas purification apparatus of the present invention,the concentration of H₂O in the gas can be adjusted prior to hydrolysisof COS. Because the gas is appropriately cooled by mixing the moisturecontent with the gas, the load on the heat exchanger for cooling thehigh-temperature gas discharged from the gasification furnace down to atemperature suitable for hydrolysis is reduced, and as a result, theheat exchanger can be reduced in size. The hydrolysis easily progressesbecause the concentration of H₂O in the gas has been adjusted, and as aresult, it is possible to reduce the amount of the COS conversioncatalyst, and thus, the COS treatment device can be reduced in size.Furthermore, because the concentration of H₂O in the gas can be adjustedafter gasification, not only raw stock that have been conventionallyused but also raw stock with high sulfur content and raw stock with alow moisture content can be used.

Next, a gas purification method of the present invention will bedescribed below.

The gas purification method of the present invention is a method ofpurifying gas that at least includes COS, H₂O, CO₂, and H₂S, and themethod at least includes an H₂O adjustment step and a COS treatmentstep. The H₂O adjustment step is a step of adjusting the concentrationof H₂O in the gas. The H₂O adjustment step is a preparation step forpreviously adjusting the concentration of H₂O in the gas to be purified,which is performed in order to degrade COS at a high degradation rate.

The COS treatment step is a step of treating and degrading COS in thegas in which the concentration of H₂O has been adjusted in the H₂Oadjustment step by hydrolysis by using the COS conversion catalyst. COShydrolytic reactions are a catalytic reaction, and it is necessary toadjust the reaction temperature according to temperature conditions thatconform to conditions for using the catalyst. More specifically, it ispreferable to adjust the temperature of the gas to a temperature in arange of 200° C. to 400° C., which is a temperature suitable forhydrolysis of COS, after adjusting the concentration of H₂O in the gasor at the same time as adjusting the concentration of H₂O in the gas.

It is preferable that the H₂O adjustment step in the gas purificationmethod according to the present invention be a step of adjusting the H₂Oconcentration so that a pressure equilibrium constant K_(P) expressed bythe following expression (1) becomes 1≦K_(P)≦20 where P_(COS) is apartial pressure of COS in the gas, P_(H2O) is a partial pressure of H₂Oin the gas, P_(CO2) is a partial pressure of CO₂ in the gas, and P_(H2S)is a partial pressure of H₂S in the gas. To vary the pressureequilibrium constant, adjustment of H₂O is the most effective means forvarying the pressure equilibrium constant considering the ease ofvariation.

[Expression 3]

K _(P)=(P _(H2S) ×P _(CO2))/(P _(COS) ×P _(H2O))  (1)

The gas purification method of the present invention can further includeat least one water washing step and at least one waste water treatmentstep. The water washing step is a step of washing the gas of which COShas been treated and degraded with water, and in this step, impuritiessuch as water-soluble halogen compounds, ammonia, organic matter, andtrace metals are removed by washing with water. In the water washingstep, the washing with water may be performed only once; however, inorder to increase the purity of the gas to be purified, the washing withwater may also be performed a plurality of times.

The waste water treatment step is a step for treating the waste water tobe drained in the water washing step, and the treatment is performed inthis step so that the waste water including the impurities that havebeen removed from the gas by washing with water can be disposed of. Morespecifically, impurities, such as halogen compounds, ammonia, organicmatter, and trace metals are treated by ammonia stripping orflocculating precipitation. It is necessary to sufficiently treatammonia, in particular, and a plurality of waste water treatment devicesmay be provided to perform an ammonia stripping treatment a plurality oftimes.

If the gas purification method of the present invention includes thewater washing step and the waste water treatment step, then the H₂Oadjustment step can be a step of mixing the water treated by the wastewater treatment step with the gas before the COS treatment step.

In the gas purification method of the present invention, the H₂Oadjustment step can be a step of mixing steam with the gas before theCOS treatment step. The step of mixing steam with the gas before the COStreatment step can be used in combination with the above-described stepof mixing the water treated by the waste water treatment step with thegas before the COS treatment step.

The gas purification method of the present invention can further includea coal drying step and a gasification step. The coal drying step is astep of drying coal by removing the moisture content from the coal. Thisstep is carried out if coal is used as a raw stock of the gas to bepurified so as to maintain the moisture content in the coal at apredetermined amount so that the gasification efficiency would notdecrease.

The gasification step is a step of gasifying the dried coal. Thegasification is performed by using oxygen, air, and oxygen-enriched airas gasification agents and thermally degrading the coal under anatmosphere of the gasification agent.

If the gas purification method of the present invention includes thecoal drying step and the gasification step, the H₂O adjustment step canbe a step of adjusting the moisture content in the coal by performingthe coal drying step. If a measurement means configured to measure themoisture content in the gasified gas is provided at an outlet of thegasification furnace, and if an adjustment means configured to adjustthe amount of heat to be introduced into the coal drying device and thedrying time for the coal in accordance with the moisture content isfurther provided, for example, H₂O can be adjusted by controlling themoisture content in the coal before gasification.

The step of adjusting the moisture content in the coal in the coaldrying step can be used in combination with the above-described step ofmixing the steam with the gas before the COS treatment step and theabove-described step of mixing the water treated by the waste watertreatment step with the gas before the COS treatment step.

In addition to the above-described steps, the gas purification method ofthe present invention can include steps such as a dust collection stepof removing dust from the gas, a temperature adjustment step ofadjusting the temperature of the gas, an H₂S recovery step of recoveringH₂S from the gas, and an absorbing solution regeneration step ofregenerating the absorbing solution that has absorbed HS.

According to the gas purification method of the present invention, theheat exchanger configured to cool the gas down to a temperature suitablefor hydrolysis can be reduced in size, the catalyst amount of the COSconversion catalyst can be reduced, and the COS treatment device can bereduced in size. In addition, because the concentration of H₂O in thegas can be adjusted after gasification, not only raw stock that has beenconventionally used, but also raw stock having a high sulfur content andraw stock with a low moisture content can be used.

Embodiments of the gas purification apparatus and the gas purificationmethod according to the present invention will be described below withreference to the drawings. Note here that the present invention is notlimited to the embodiments illustrated in the drawings.

FIG. 1 is an outline view of a gas purification process 1-1. In thisprocess, first, coal 2 is gasified by a gasification furnace 4 in thepresence of a gasification agent 3. The gas having been obtained bygasifying the coal at least includes COS, H₂O, CO₂, and H₂S, andimpurities such as halogen compounds are also contained therein. Theobtained gas is purified by converting COS in the obtained gas into H₂Sby using a COS treatment device 5, removing impurities by using a waterwashing column 6 a, and then recovering H₂S from the gas by using an H₂Sabsorption column 7. The purified gas is used for chemical productsynthesis 8 for synthesizing chemical products such as methanol andammonia or is introduced into gas turbines or steam turbines forelectric power generation by using an electric power generation device9. A waste water treatment device 10 a is configured to treat wastewater drained from the water washing column 6. Some of the treated wastewater is fed from the waste water treatment device 10 via a feed line 12a into an introduction line 11 for introducing the gas from thegasification furnace 4 into the COS treatment device 5, and thereby, H₂Oin the gas before being introduced into the COS treatment device 5 isadjusted.

FIG. 2 is an outline view of a gas purification process 1-2, which is aprocess that includes a water washing column 6 b, a waste watertreatment device 10 b, and a feed line 12 b in addition to theconfiguration of the gas purification process illustrated in FIG. 1.Considering influences on COS conversion catalysts imparted by halogencompounds in the waste water, the waste water from the waste watertreatment device 10 a is released. The waste water from the waste watertreatment device 10 b containing less impurities is introduced into thegas before being introduced into the COS treatment device 5.

FIG. 3 is an outline view of a gas purification process 1-3, which is anembodiment different from those illustrated in FIGS. 1 and 2. In thisprocess, H₂O in the gas before being introduced into the COS treatmentdevice 5 is adjusted by feeding steam from a boiler 13 into theintroduction line 11 via a feed line 14. In addition, H₂O in the gas canbe adjusted by bleeding steam from a steam turbine 15 and feeding thegas via a route indicated by arrows A in the drawing or can be adjustedalso by feeding a part of feed water 30 to be fed into a waste waterrecovery boiler 16 via a route indicated by arrows B in the drawing.

FIG. 4 is an outline view of a gas purification process 1-4, which is anembodiment different from those illustrated in FIGS. 1 to 3. Moisture isremoved from the coal 2 by using a coal drying device 17 to dry the coal2, and the dried coal 2 is then introduced into the gasification furnace4. The drying of the coal is carried out by using heat from the flue gasintroduced from flue gas 18 for drying. In this gas purification process1-4, the temperature and the feeding amount of the flue gas, the dryingtime for the coal, and the like are controlled, and thus, some of themoisture content is discharged to an outside of the system and the coal2 with the moisture content being maintained is introduced into thegasification furnace, and thereby H₂O in the gas is adjusted.

FIG. 5 is an outline view of the gas purification process 1-5, which isan embodiment provided with all the H₂O adjustment means illustrated inFIGS. 1 to 4. The introduction of the waste water from the waste watertreatment device, the introduction of steam from the boiler, and theintroduction of the moisture content performed by controlling drying ofthe coal can be individually controlled so that H₂O in the gas isappropriately adjusted in accordance with the state of the purificationof the gas.

FIG. 6 is a diagram that illustrates an example of a gas purificationapparatus 20 according to the present embodiment. The gas purificationapparatus 20 is a gas purification apparatus corresponding to theoutline view of the gas purification process 1-2 illustrated in FIG. 2.The gas purification apparatus 20 has a basic configuration includingthe gasification furnace 4, a dust collecting device 21, heat exchangers22 and 23, the COS treatment device 5, the water washing columns 6 a and6 b, the waste water treatment devices 10 a and 10 b, the H₂S absorptioncolumn 7, and an absorbing solution regeneration column 24.

In this gas purification apparatus 18, first, the coal 2 is gasified bythe gasification furnace 4 in the presence of the gasification agent 3.The gas obtained by gasification of the coal at least contains COS, H₂O,CO₂, and H₂S, and impurities such as halogen compounds and dust are alsocontained therein. Dust is removed from the obtained gas first by usingthe dust collecting device 21, and then, the gas is cooled by the heatexchanger 22 to a temperature in a range of 200° C. to 400° C., which isa temperature suitable for hydrolysis of COS. Next, COS in the gas isconverted by the COS treatment device 5 into H₂S, heat is recovered bythe heat exchanger 23, then impurities are removed therefrom by usingthe water washing columns 6 a and 6 b, and then H₂S is recovered by theH₂S absorption column 7 from the gas to purify the gas. The temperatureof the gas is low after the purification, and the purified gas isintroduced into the electric power generation device 9 via the heatexchangers 22 and 23 while being used for cooling of the gas dischargedfrom a dust collecting device 19 or the COS treatment device 5, and heatis thus recovered from the purified gas. After having absorbed H₂S inthe H₂S absorption column 7, the absorbing solution is regenerated bybeing separated from H₂S 25, of which the concentration has become highin the absorbing solution regeneration column 24, and the regeneratedsolution is fed into the H₂S absorption column 7. The waste watertreatment device 10 a, 10 b treats the waste water drained from thewater washing column 6 a, 6 b. Some of the treated waste water is fedfrom the waste water treatment device 10 b via the feed line 12 into theintroduction line 11 for introducing the gas from the dust collectingdevice 21 into the COS treatment device 5, and thereby, H₂O in the gasbefore being introduced into the COS treatment device 5 is adjusted. Theamount of the waste water to be fed is measured by moisture contentmeasuring devices 26, which are provided at locations across a locationof mixing the waste water from the feed line 12 and configured tomeasure the moisture content contained in the gas that passes throughthe introduction line 11, and the amount of the waste water is adjustedby opening and closing a control valve 27 in accordance with themoisture content. The measuring device 26 is capable of measuring thecontent of COS, CO₂, and H₂S in addition to the moisture content in thegas. On the basis of measurement values obtained by the measuringdevices 26, H₂O can be adjusted so that the pressure equilibriumconstant (K_(P)), which is calculated based on the partial pressure ofCOS in the gas (P_(COS)), the partial pressure of H₂O (P_(H2O)), thepartial pressure of CO₂ (P_(CO2)), and the partial pressure of H₂S(P_(H2S)), becomes 1≦K_(P)≦20. The waste water can be vaporized by theheat from the gas. Alternatively, the waste water can be vaporized priorto mixing of the waste water with the gas.

In the gas purification apparatus according to the present embodiment,for the gasification furnace, a fixed type gasification furnace, a flowtype gasification furnace, a jet stream type gasification furnace, andthe like can be used. For the dust collecting device, a cyclone typedust collecting device, a filtering type dust collecting device, and thelike can be used. For the heat exchangers, a shell and tube type heatexchanger and the like can be used.

In the gas purification apparatus according to the present embodiment,for the COS treatment device, a device in which a COS conversioncatalyst is loaded in an inside of the reactor can be used, for example.For the COS conversion catalyst, a honeycomb-shaped catalyst can beused, and catalysts with a pellet-like shape can also be used, and COSis converted into H₂S when the gas passes through the catalyst.

Next, for the water washing column, a water washing column can be usedwhich includes a configuration in which washing water is fed from anupper portion in the water washing column and washing water that hasaccumulated in a lower portion is circulated by using a circulation pumpto be fed therefrom, for example.

For the waste water treatment device, a waste water treatment device canbe used which includes a configuration including an ammonia strippingcolumn and a flocculating precipitation device. The ammonia strippingcolumn is a device configured to remove ammonia with a highconcentration contained in the waste water by dispersing it in the gasphase by blowing steam or air therein. The ammonia stripping column isconstituted by a perforated plate and a downcomer provided in itsinside, for example, and the waste water flows down from an upper stageto a lower stage via the downcomer. In contrast, the steam flows up fromthe lower stage to the upper stage through the holes of the perforatedplate and rises in the liquid that has been dammed on the perforatedplate. The waste water and the steam are thus brought into contact witheach other and the ammonia dissolved in the waste water is transferredto the steam. The dissipated ammonia is degraded by oxidation through acatalytic reaction column in which a catalyst has been loaded, forexample, and the degraded substance is then released into the atmosphereas harmless nitrogen gas. On the other hand, the flocculatingprecipitation device is constituted by a flocculation tank and aprecipitation tank, for example. In the flocculation tank, the wastewater and a flocculant such as aluminum sulfate and polyaluminumchloride are mixed together, and thus, impurities are coagulated andflocculated. In the precipitation tank, the flocculated substances areallowed to precipitate to separate the precipitate into precipitated andflocculated substances and treat water. The waste water is treated byusing the ammonia stripping column and the flocculating precipitationdevice.

The H₂S absorption column can be provided with a configuration in whichan amine compound absorption solution, which is constituted by anaqueous solution of an amine compound, is fed from an upper portion inan inside of the H₂S absorption column and also the absorbing solutionthat has accumulated in a lower portion of the column is circulated byusing a circulation pump to be fed therefrom.

The absorbing solution regeneration column can be provided with aconfiguration in which the absorbing solution that has absorbed H₂S isheated by a reboiler, then the solution is cooled by a cooler beforebeing separated into H₂S and an amine compound absorbing solution, andthen the amine compound absorbing solution is fed into the H₂Sabsorption column by using a pump.

In the gas purification apparatus 18 illustrated in FIG. 6, the gas isappropriately cooled by mixing the moisture content with the gas beforeperforming hydrolysis of COS. Thus, the load on the heat exchanger 20for cooling the high-temperature gas discharged from the gasificationfurnace is reduced, and as a result, the heat exchanger 20 can bereduced in size. It becomes easy for the hydrolysis to progress becausethe concentration of H₂O in the gas has been adjusted, and as a resultof this, it is enabled to reduce the catalyst amount of the COSconversion catalyst 26, and thus, the COS treatment device 5 can bereduced in size. Furthermore, because the concentration of H₂O in thegas can be adjusted after the gasification, not only coal 2 that hasbeen conventionally used, but also coal with high sulfur content andcoal having a low moisture content can be used.

INDUSTRIAL APPLICABILITY

According to the gas purification apparatus and the gas purificationmethod of the present invention, the treatment for degrading COS can bepromoted by adjusting the concentration of H₂S of the material gaswithout decreasing the thermal efficiency, and accordingly, the presentinvention is industrially useful.

REFERENCE SYMBOLS LIST

-   1-1 Gas purification process-   1-2 Gas purification process-   1-3 Gas purification process-   1-4 Gas purification process-   1-5 Gas purification process-   2 Coal-   3 Gasification agent-   4 Gasification furnace-   5 COS treatment device-   6 a, 6 b Water washing column-   7 H₂S absorption column-   8 Synthesis of chemical product-   9 Electric power generation device-   10 a, 10 b Waste water treatment device-   11 Introduction line-   12 a, 12 b Feed line-   13 Boiler-   14 Feed line-   15 Steam turbine-   16 Waste water recovery boiler-   17 Coal drying device-   18 Flue gas for drying-   19 Steam-   20 Gas purification apparatus-   21 Dust collecting device-   22 Heat exchanger-   23 Heat exchanger-   24 Absorbing solution regeneration column-   25 High-concentration H₂S-   26 Measuring device-   27 Control valve-   28 COS conversion catalyst-   29 Gas turbine-   30 Feed water

1-10. (canceled)
 11. A gas purification apparatus configured to purifygas at least including COS, H₂O, CO₂, and H₂S, the apparatus at leastcomprising: a COS treatment device comprising a COS conversion catalystand configured to degrade COS in the gas by hydrolyzing; H₂O adjustmentmeans configured to adjust a concentration of H₂O in the gas to beintroduced into the COS treatment device; a coal drying deviceconfigured to dry coal by removing moisture from the coal; and agasification furnace configured to gasify the dried coal, wherein theH₂O adjustment means is configured to adjust the moisture content in thecoal by using the coal drying device.
 12. The gas purification apparatusaccording to claim 11, wherein the H₂O adjustment means is meansconfigured to adjust the concentration of H₂O so that a pressureequilibrium constant K_(P) expressed by the following expression (1)becomes 1≦K_(P)≦20:[Expression 1]K _(P)=(P _(H2S) ×P _(CO2))/(P _(COS) ×P _(H2O))  (1) where P_(COS) is apartial pressure of COS in the gas, P_(H2O) is a partial pressure of H₂Oin the gas, P_(CO2) is a partial pressure of CO₂ in the gas, and P_(H2S)is a partial pressure of H₂S in the gas.
 13. The gas purificationapparatus according to claim 11, further comprising: at least one waterwashing device configured to wash the gas discharged from the COStreatment device with water; and at least one waste water treatmentdevice configured to treat the waste water discharged from the waterwashing device, wherein the H₂O adjustment means is configured to mixwater from the waste water treatment device with the gas to beintroduced into the COS treatment device.
 14. The gas purificationapparatus according to claim 11, wherein the H₂O adjustment means isconfigured to mix steam with the gas to be introduced into the COStreatment device.
 15. A gas purification method for purifying gas atleast including COS, H₂O, CO₂, and H₂S, the method at least comprising:an H₂O adjustment step of adjusting a concentration of H₂O in the gas; aCOS treatment step of degrading COS in the gas of which theconcentration of H₂O has been adjusted by hydrolyzing by using a COSconversion catalyst; a coal drying step of drying coal by removingmoisture from the coal; and a gasification step of gasifying the driedcoal, wherein the H₂O adjustment step is a step of adjusting themoisture content in the coal in the coal drying step.
 16. The gaspurification method according to claim 15, wherein the H₂O adjustmentstep is a step of adjusting the concentration of H₂O so that a pressureequilibrium constant K_(P) expressed by the following expression (1)becomes 1≦K_(P)≦20:[Expression 2]K _(P)=(P _(H2S) ×P _(CO2))/(P _(COS) ×P _(H2O))  (1) where P_(COS) is apartial pressure of COS in the gas, P_(H2O) is a partial pressure of H₂Oin the gas, P_(CO2) is a partial pressure of CO₂ in the gas, and P_(H2S)is a partial pressure of H₂S in the gas.
 17. The gas purification methodaccording to claim 15, further comprising: at least one water washingstep of water washing the gas obtained by degrading COS; and at leastone waste water treatment step of treating waste water discharged in thewater washing step, wherein the H₂O adjustment step is a step of mixingthe water treated by the waste water treatment step with the gas beforethe COS treatment step.
 18. The gas purification method according toclaim 15, wherein the H₂O adjustment step is a step of mixing steam withthe gas before the COS treatment step.
 19. The gas purificationapparatus according to claim 12, further comprising: at least one waterwashing device configured to wash the gas discharged from the COStreatment device with water; and at least one waste water treatmentdevice configured to treat the waste water discharged from the waterwashing device, wherein the H₂O adjustment means is configured to mixwater from the waste water treatment device with the gas to beintroduced into the COS treatment device.
 20. The gas purificationapparatus according to claim 12, wherein the H₂O adjustment means isconfigured to mix steam with the gas to be introduced into the COStreatment device.
 21. The gas purification apparatus according to claim13, wherein the H₂O adjustment means is configured to mix steam with thegas to be introduced into the COS treatment device.
 22. The gaspurification method according to claim 16, further comprising: at leastone water washing step of water washing the gas obtained by degradingCOS; and at least one waste water treatment step of treating waste waterdischarged in the water washing step, wherein the H₂O adjustment step isa step of mixing the water treated by the waste water treatment stepwith the gas before the COS treatment step.
 23. The gas purificationmethod according to claim 16, wherein the H₂O adjustment step is a stepof mixing steam with the gas before the COS treatment step.
 24. The gaspurification method according to claim 17, wherein the H₂O adjustmentstep is a step of mixing steam with the gas before the COS treatmentstep.